1. Technical Field of the Invention
The invention relates to optical elements and methods. More specifically, the invention relates to an optical beamsplitter that can be used to propagate optical signals.
2. Description of the Related Art
A beamsplitter is an optical device that receives an incident light beam and divides it into two components. The first component is propagated from the beamsplitter as a transmitted beam. The second component is propagated as a reflected optical beam angularly displaced from the transmitted beam.
A conventional beamsplitter comprises a cube of optically-transparent material encasing a thin layer of semi-reflecting material oriented diagonally across the interior. About one-half of the light entering a face of the beamsplitter is reflected by the semi-reflecting material through an adjacent face as a reflected light beam. The remaining portion of the incident light beam is transmitted by the layer of semi-reflecting material through the opposite face as a transmitted light beam.
Beamsplitters are used in optical devices such as scanners, interferometers and back-scattering detectors for measuring back-scatter from particles. A problem associated with conventional cubic beamsplitters is distortion caused by light striking faces at oblique, i.e. non-perpendicular, angles. Transmission through the beamsplitter is refracted at the surface according to Fresnel's Equations. The refracted light beam is parallel to the incident beam and displaced from it. The magnitude of displacement depends on the angle of incidence and the index of retraction of optical materials in beamsplitter components. This distortion may be compensated for to some extent by repositioning components in an optical system.
U.S. Pat. No. 6,411,441 to Gorden Videen discloses a Beamsplitter Prism with Cylindrical Faces for Transmitting or Reflecting Cylindrical Waves Without Magnification.